1. Field of the Invention
The present invention relates to a softening point measuring apparatus using a scanning probe microscope as a base, for measuring a softening point (glass transition or melting point) of a sample by detecting a flection amount of a cantilever when a contacting portion with the sample is locally heated using a heat generating portion provided to the cantilever. In addition, the present invention relates to a thermal conductivity measuring apparatus using a scanning probe microscope as a base, for measuring thermal conduction of a sample surface via the contacting portion with the sample by detecting temperature variation of the cantilever from a change in resistance of the heat generating portion of the cantilever.
2. Description of the Related Art
A conventional apparatus for measuring a softening point such as glass transition or melting point of a sample by locally heating a sample surface includes a probe having a heat generating portion, a function of heating the heat generating portion, a light source which projects light to a mirror for detecting a position provided to the probe, a detector which detects reflected light that is projected from the light source and reflected by the mirror so as to convert the same into an electric signal, and a circuit which uses an output signal of the detector as a flection displacement signal of the probe. The probe tip is brought into contact with the sample surface, and the heat generating portion is heated, so that the contacting portion with the sample surface is heated. When the temperature becomes the softening point such as glass transition or melting point in accordance with the material of the sample, the probe sinks in the sample surface. This is detected as a flection displacement signal of the probe so that the softening point is measured (Japanese Patent Translation Publication No. Hei 11-509003).
In addition, a conventional apparatus for measuring thermal conduction of a sample includes a probe having a heat generating portion, a function of measuring a resistance of the heat generating portion, a light source which projects light to a mirror provided to the probe, a detector which detects reflected light that is projected from the light source and reflected by the mirror so as to convert the same into an electric signal, and a circuit which uses an output signal of the detector as a flection displacement signal of the probe. The heat generating portion of the probe is heated, a resistance value is detected, and the probe tip is brought into contact with a sample surface so as to scan the sample surface. Then, thermal flow from the probe to the sample changes in accordance with thermal conduction distribution in the sample surface so that temperature of the heat generating portion changes, which results in a variation of the resistance. Therefore, by detecting the resistance, thermal conduction distribution or the like in the sample surface may be measured (Japanese Patent Translation Publication No. Hei 11-509003).
In addition, a platinum wire or the like is used as the probe. A diameter of the wire is 6 μm and a probe tip has a tip curvature radius of 5 μm, which are too thick to realize nanometer order resolution. Instead of a manual process using the platinum wire or the like, a semiconductor process has been developed for manufacturing a cantilever made of silicon as a substitution of the wire probe.
Therefore, there are increasing cases where a cantilever made of silicon is used for a purpose of local heating, local thermal conduction measurement, or the like.
There is manufactured a cantilever made of silicon for local heating, in which heat generating portion is a doped resistor. A doped portion is made to generate heat so as to heat the sample surface locally, and a softening point of the sample is measured. There is manufactured a cantilever having a probe tip sharpened by etching of a semiconductor process (US Patent No. 20,060,254,345).
In addition, a cantilever made of silicon for measuring thermal conduction has a patterned wiring of metal thin film formed on the cantilever tip. The cantilever is heated at a constant temperature and is brought into contact with the sample surface by the probe which was comprised on the cantilever tip so as to scan the same. Then, a degree of thermal flow into the sample surface is detected as a resistance variation of the metal thin film pattern so that thermal conduction distribution or the like is measured. The cantilever of the metal thin film pattern is also manufactured by the semiconductor process (Japanese Patent Application Laid-Open No. Hei 07-325092).
The cantilever made of silicon is manufactured by the semiconductor process, and the probe tip is sharpened to be of 10 nmR or the like. The cantilever made of silicon is manufactured for heating locally or measuring local thermal conduction and is being used also in nanotechnology fields for thermal analysis.
However, it was found that even if the probe tip of the cantilever made of silicon is sharpened to be of approximately 10 nmR by the semiconductor process, measuring of the softening point or the local thermal conduction is difficult by locally heating the sample.
When the local heating is performed, the heat generating portion is heated so that the contacting portion with the sample is heated by thermal conduction to the probe. The probe tip has a curvature radius of 10 nmR, and the side surface of the probe has a pyramidal shape so as to form a surface. Therefore, the side surface of the probe is also heated, and heat of the heat generating portion is conducted from the probe to the sample contacting portion and is also dissipated via air from the side surface of the probe. Thus, it is found that the heat also affects the periphery of the probe contacting portion.
In the measurement of a softening point, if it is desired to compare characteristics of neighboring measurement points, heating operation at a first measurement point gives thermal history to the sample surface at the peripheral portion, and at the next measurement point, measurement of the softening point is performed after being affected by the thermal history, so that correct comparison of physical properties may not be performed. If the heat diffusion via air is taken into account, thermal influence by the heated probe causes substantially the same effect as that of a thicker probe despite of the sharpened probe tip.
In addition, when the thermal conduction is measured, the sample surface is scanned by the probe while detecting the resistance of the heated heat generating portion. The detection range of the resistance is not limited to the contacting portion between the probe and the sample surface but covers the range that is affected by the thermal influence due to the above-mentioned thermal dissipation from the side surface of the probe. Therefore, the thermal conduction may not be measured correctly. In addition, it was found that if the sample surface has a level difference, thermal dissipation occurs in the same manner as described above when the side surface portion of the probe becomes close to the uneven part due to the level difference, and therefore thermal conduction thereof becomes different apparently despite that the surface is uniform in material, so that the thermal conduction distribution may not be measured correctly.